The present invention relates to a bolt wherein oblique screwing of said bolt into a nut is prevented. More particularly, the present invention relates to a bolt having a threaded shank portion wherein a notch slanting toward the end of said threaded shank portion at an angle in the range between 15xc2x0 to 80xc2x0 for the axis of said threaded shank portion is formed at the beginning of the complete thread part of said thread shank portion.
It has been known that the encroaching, the seizure, or the racing between the bolt and the nut is caused by the oblique screwing of a bolt into the nut. Hitherto a bolt having a guide boss (204) has been provided as shown in FIG. 5. Said bolt (201) consists of a head portion (202), a shank portion (203) on which a thread part (203A) is formed (a threaded shank portion) and a guide boss (204) extended from the end of said shank portion (203). And the outer diameter Db of said guide boss (204) is settled to be a little smaller than the inner diameter Dn of a nut (105) into which said bolt (201) is screwed.
By employing said bolt (201) having a guide boss (204), the oblique screwing of said bolt (201) of said nut (105) is passably prevented because when said bolt (201) is screwed into said nut (105), said guide boss (204) whose outer diameter Db is a little smaller than the inner diameter Dn of said nut (105) is first inserted into the threaded hole (105A) of said nut (105).
Nevertheless in said traditional bolt (201), a little play exists between said guide boss (204) of said bolt (201) and the inside (105C) of said nut (105) such that the oblique screwing can not be prevented completely. And the problems of the encroaching, the seizure, and the racing are still not dissolved.
Accordingly, an object of the present invention is to dissolve effectively the problems of the encroaching, the seizure, and the racing.
Said object can be attained by employing a bolt having a threaded shank portion wherein a notch slanting toward the end of said threaded shank portion at an angle in the range between 15xc2x0 to 80xc2x0 for the axis of said threaded shank portion is formed at the beginning of the complete thread part of said thread shank portion.
Preferably said thread rises from the beginning of the thread part attaining to the height of the complete thread within the range from the beginning of the thread part to a position revolving at 50xc2x0 from the beginning of the thread part.
Further, preferably said expanded width of the entrance of the thread part is set to be larger than the pitch of thread part and smaller than 1.5 times of the pitch of the thread part.
Still further preferably a guide boss is extended from the end of said shank part.
Still further preferably a spiral guide is formed on said guide boss, said spiral guide groove continuing to the root of the thread part of said threaded shank portion and being deeper than the root of the thread part excepting the boss end parts of said spiral guide groove.
Since said notch (103B) slanting to the end of said threaded shank portion is formed at the beginning of the complete thread part of the thread part (103A) to expand the width W of the entrance (103E) of the thread part, the entrance (103E) of the thread having an expanded width W is smoothly guided by the thread (105B) of said nut (105), and the oblique screwing of said bolt (101) is corrected by said notch (103B) when said bolt (101) is obliquely screwed into the threaded hole (105A) of said nut (105). In a case where a guide boss (104) is extended from the end of said shank portion (103) of said bolt (101), when said bolt (101) is obliquely screwed into the threaded hole (105A) of said nut (105), said oblique screwing is previously corrected by said guide boss (104) such that the correction of said oblique screwing by said entrance having an expanded width W of the thread part (103A) of said bolt (101), and said notch (103B) is more smoothly performed. Further, in a case where a spiral guide groove (104A) is formed on said guide boss (104), said spiral guide groove (104A) is screwed into the thread (105B) of said nut (105) and guided such that the previous correction of oblique screwing of said bolt (101) is more smoothly performed.